The importance of correct chiller design & installation from the outset
A recent remediation project in Surrey highlights the critical importance of designing and installing HVAC equipment correctly at the outset.
A pair of Rhoss Turbocor TCATBZ2700 packaged air-cooled water chillers that supply chilled water to air handling units and fan coil units at multinational consumer goods giant, Procter & Gamble’s Weybridge headquarters site were poorly designed and badly fitted when they were first installed 12 years ago.
This prompted engineers to report that they performed inefficiently and were suffering from compressor problems which dramatically reduced their cooling capacities and, therefore, their efficiency.
Getting the best out of state-of-the-art chillers
Under normal operating conditions, and with effective design and installation, TCATBZ2700 chillers with axial fans chillers perform exceptionally well. They employ state-of-the-art technology including Turbocor oil-free centrifugal compressors, which combine high efficiency with whisper-quiet operation.
A flooded-type evaporator enhances their performance and efficiency still further.
Turbocor centrifugal compressors – the first in the world to feature oil-free operation for heating and cooling – offer outstanding energy efficiency, significantly reduce running costs, and help shrink a facility’s carbon footprint thanks to annual energy consumption that is 30 to 50% less than conventional compressors.
The ventilating section of the chillers allows excellent heat exchange with low noise levels and the electronic expansion valve ensures precise, quick regulation under a range of different load conditions.
Paul King, project sales manager at LH-plc: “We carried out an airflow test and noise test. The report showed the plant room was in a vacuum environment due to airflow restrictions. Not enough air was available to match the chiller airflow requirements.”
Poor install compromises chiller performance
However, the two chillers at Procter & Gamble’s HQ were sited and installed particularly poorly. The technologically advanced devices are designed to be located outside, typically on a roof or in a chiller compound. But they were installed in a basement plantroom with ducting to create an airflow path.
Consequently, the chillers displayed extremely high head pressures and poor coefficients of performance (CoPs) because, in normal operation, the chillers were forced to run at 100% all the time to cope with the building’s heat load requirements.
Moreover, numerous compressor changes were required because the compressors had to work so hard, and this resulted in premature failure due to the high head pressures and poor airflows.
Furthermore, the cooling line to the compressors was too small, causing flash gas to reach the inverter which triggered overheating and a forced reduction in speed in order to safeguard the compressors. This, in turn, meant they failed to operate at their optimum level.
Testing chiller performance
Paul King, project sales manager at LH-plc, explained: “We carried out an airflow test and noise test. The report showed the plant room was in a vacuum environment due to airflow restrictions. Not enough air was available to match the chiller airflow requirements.”
Another issue that meant the compressor lost efficiency was that a suction line to the compressors was constructed with too many bends, which caused high velocity gas to reach the impeller with high turbulence.
Meanwhile, the air intake to the plant room was channelled through a sound attenuator which restricted its flow, creating high resistance and poor airflow to the condenser.
To make matters worse, the hot air discharged into a plenum with no separation between the two chillers to facilitate air recirculation. This, and the very high discharge pressure, caused the compressors to work to their maximum speed most of the time. This resulted in high energy use and compressor failures.
“The chillers now operate with a coefficient of performance (CoP) of 1.8 compared with 1.4 before the improvements. In other words, it is now twice as efficient as previously." Paul King, LH-Plc
- Airflow and noise test, which showed the plant room was in a vacuum environment
- Replacement of compressor suction line, which had too many bends causing high velocity gas to reach the impeller
- Correcting air intake, which was channelling through a sound attenuator with restricted flow
- Implementation of separation between the two chillers and hot air discharge
- Reduction of discharge pressure to reduce energy consumption and the risk of compressor failure
To upgrade the installation, LH-plc has supplied and fitted a wall divider and removed two ducting components not required to allow improved airflow plus carried out chiller refrigeration circuit modifications to further enhance operation.
The suction line problem was rectified by reducing the number of bends and fabricating the pipe in order to reduce gas turbulence before the impeller.
“The modified chiller installation has resulted in a vast improvement in air onto and away from the chiller condenser coils plus the compressor pipework modifications. The energy savings and less strain on compressors will mean big money savings. They will run for less time and, when they are operating, they won’t run at a constant 100% as they were previously,” concluded Paul.